The present invention relates to a target of sintered compact containing a Vb-group element (A) and a chalcogenide element (B), or containing the elements (A) and (B) and additionally a IVb-group element and/or a IIIb-group element (C), in which the electric resistivity of the sintered compact is reduced, as well as to a method of producing such a target. Note that this material containing a Vb-group element (A) and a chalcogenide element (B), or containing the elements (A) and (B) and additionally a IVb-group element and/or a IIIb-group element (C), in which the electric resistivity of the sintered compact is reduced, is hereinafter abbreviated as the “Ge—Sb—Te-based material”.
In recent years, a thin film formed from the Ge—Sb—Te-based material is being used as a material for phase-change recording; that is, as a medium for recording information by using phase transformation.
As a method of forming this thin film of the Ge—Sb—Te-based alloy material, it is standard to use a means generally referred to as a physical vapor deposition method such as the sputtering method. In particular, the thin film is often formed using the magnetron sputtering method from the perspective of operability and film stability.
Formation of films by the sputtering method is performed by physically colliding positive ions such as Ar ions to a target located on a cathode side, ejecting materials configuring the target with the collision energy, and laminating a film similar in composition to the target material onto the anode-side substrate that is located opposite to the target.
The coating method based on the sputtering method has a feature that enables to form films of various thicknesses; for instance, from a thin film of angstrom units to a thick film of several ten μm; with a stable deposition rate by adjusting the processing time, power supply and the like.
Attention has been conventionally focused on inhibiting the generation of particles in order to stably and efficiently perform sputtering, and a high-density sintered compact having a relative density of approximately 98.8% has been prepared by sintering, via hot press, the raw powder having high purity and a prescribed grain size.
As a sintered compact of the Ge—Sb—Te-based material, known is a sintered compact that is obtained by appropriately combining a chalcogenide element (S, Se, Te), a Vb-group element (Bi, Sb, As, P, N), a IVb-group element (Pb, Sn, Ge, Si, C) and an additive element (Ag, Au, Pd, Pt, B, Al, Ti, Zr, Zn) to be sintered.
Nevertheless, these materials generally have low thermal conductivity and low electric conductivity. For example, with a Ge2Sb2Te5 alloy that is generally used as a material for a phase-change memory, there have been only those having electric resistivity exceeding 0.26 mΩ·cm.
A target produced from this kind of sintered compact with low thermal conductivity and low electric conductivity often entails such problems particularly caused by low thermal conductivity where components with high vapor pressure become volatilized and particles are generated easily due to the heat generated by the sputtering being accumulated within the target.
In addition, there is a problem such as charge-up with DC sputtering, and it is necessary to take measures such as using the pulsed DC sputtering technique to perform the deposition. Still, it is impossible to completely eliminate drawbacks such as arcing caused by the charge-up, and there is a problem in that the deposition efficiency is low.
As conventional technology, known is a technique of increasing the concentration of oxygen contained in the film in order to deposit a GeSbTe film with high electric resistivity (refer to Patent Document 1). In Patent Document 1, a Ge—Sb—Te target is prepared, and the oxygen partial pressure is adjusted so as to form, by DC magnetron sputtering, a phase-change recording film with high electric resistance in which the oxygen in the film is increased to 0.1 to 15%.
With the oxygen during the deposition, Ar+O2 atmosphere is used as the sputtering atmosphere, and oxygen is introduced into the film therefrom. However, since oxygen is consumed during the deposition process, there is a problem in that the amount of oxygen will fluctuate during the deposition unless the amount of oxygen gas in the sputtering atmosphere is strictly controlled. As a technique for dealing with this problem, for example, proposed is to produce a sputtering target to which oxygen has been preliminarily introduced (refer to Patent Document 2).
In addition, proposed is a Ge—Sb—Te-based sputtering target containing 0.3 to 1.5% of oxygen in order to improve the resistance to sputtering cracks so that the target will not crack even when sputtering is performed with high power (refer to Patent Document 3).
The simple introduction of oxygen is one index with respect to the point that the electric resistivity and resistance to sputtering cracks will change, but it is considered that the thermal resistance and electric resistance will increase due to ceramization (oxidation), and the same effect applies to Patent Document 1. Thus, this technology is heading in a direction that is opposite to improving the electric conduction and thermal conduction, and cannot be used as a technical guideline for increasing the thermal conductivity and electric conductivity of the target in order to perform stable DC sputtering.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-311729    [Patent Document 2] Japanese Laid-Open Patent Publication No. H11-286773    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2004-323919